Reporting of channel quality indicators for a non-linear detector

ABSTRACT

Techniques for determining channel quality indicators (CQIs) for a non-linear detector at a user equipment (UE) are described. In one design, the UE may determine at least one parameter (e.g., at least one threshold) based on at least one constellation constrained capacity function. Each threshold may correspond to a maximum number of information bits for one stream when a particular modulation order is used for another stream. The UE may determine CQIs for multiple streams for the non-linear detector based on the at least one parameter. The UE may also select a precoding matrix (e.g., jointly with the CQIs) based on the at least one parameter. The UE may report the selected precoding matrix and the CQIs for the multiple streams. The UE may thereafter receive a transmission of the multiple streams, which may be transmitted based on the selected precoding matrix and the CQIs.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for reporting channel quality indicators(CQIs) in a wireless communication network.

II. Background

Wireless communication networks are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks.

A wireless communication network may include a number of base stationsthat can support communication for a number of user equipments (UEs). AUE may communicate with a base station via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase station to the UE, and the uplink (or reverse link) refers to thecommunication link from the UE to the base station.

A base station may transmit data via a wireless channel to a UE. Goodperformance may be achieved by having the UE estimate the receivedsignal quality of the wireless channel, determine one or more CQIs forone or more data streams based on the received signal quality and theUE's processing capability, and report the CQI(s) to the base station.The base station may then transmit data based on the reported CQI(s).Data transmission performance may be dependent on the accuracy of thereported CQI(s). There is therefore a need in the art for techniques toefficiently and accurately determine CQI(s) in a wireless communicationnetwork.

SUMMARY

Techniques for determining CQIs for a non-linear detector at a UE (orsome other entity) are described herein. A non-linear detector may beused to receive multiple data streams transmitted simultaneously via amultiple-input multiple-output (MIMO) channel and may have betterperformance than a linear detector. However, estimation of receivedsignal quality for a non-linear detector may be much more complex thanfor a linear detector. Accurate and efficient determination of CQIs mayenable the UE to obtain the better performance of the non-lineardetector.

In one design, the UE may determine at least one parameter based on atleast one constellation constrained capacity function. The UE maydetermine CQIs for multiple streams for a non-linear detector based onthe at least one parameter. The UE may also select a precoding matrix(e.g., jointly with the CQIs) based on the at least one parameter. TheUE may report the selected precoding matrix and the CQIs for themultiple streams. The UE may thereafter receive a transmission of themultiple streams, which may be transmitted based on the selectedprecoding matrix and the CQIs.

In one design, the multiple streams may comprise a first stream and asecond stream. In one design, the UE may determine at least one firstthreshold for the first stream and at least one second threshold for thesecond stream based on the at least one constellation constrainedcapacity function. Each first threshold may be associated with adifferent modulation order and may correspond to a maximum number ofinformation bits for the first stream when the associated modulationorder is used for the second stream. Similarly, each second thresholdmay be associated with a different modulation order and may correspondto a maximum number of information bits for the second stream when theassociated modulation order is used for the first stream. For example,the UE may determine (i) three first thresholds for the first stream forthree modulation orders of QPSK, 16-QAM, and 64-QAM for the secondstream and (ii) three second thresholds for the second stream for threemodulation orders of QPSK, 16-QAM, and 64-QAM for the first stream. Thefirst and second thresholds may relate to transport block size (TBS), orsignal-to-noise-and-interference ratio (SINR), or some other parameter.The UE may determine the first and second thresholds based further on aprecoding matrix, a channel matrix, and a noise covariance matrix, asdescribed below. The UE may determine a pair of first and secondthresholds associated with the highest overall throughput and maydetermine CQIs for the first and second streams based on this pair offirst and second thresholds.

In one design, a base station may receive the CQIs and the precodingmatrix from the UE. The base station may transmit the multiple streamsto the UE based on the CQIs and the precoding matrix.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a block diagram of a transmitter.

FIG. 1B shows a block diagram of a receiver.

FIG. 2 shows a diagram of two CQIs for two streams.

FIGS. 3A and 3B show plots of BLER contours for two streams.

FIGS. 4A to 4C show plots of feasible BLER regions for two streams.

FIG. 5 shows plots of TBS thresholds for one stream.

FIG. 6 shows a plot of a feasible BLER region for one stream based onSINR.

FIG. 7 shows a process for determining CQIs for two streams.

FIG. 8 shows a process for reporting CQIs.

FIG. 9 shows an apparatus for reporting CQIs.

FIG. 10 shows a process for receiving CQIs.

FIG. 11 shows an apparatus for receiving CQIs.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA, which employs OFDMA on the downlink and SC-FDMA on theuplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, certain aspects of the techniquesare described below for a CDMA network, which may utilize WCDMA,cdma2000, or some other CDMA radio technology.

The techniques described herein may also be used for MIMO transmissionon the downlink as well as the uplink. The techniques may be used totransmit S data streams simultaneously from multiple (T) transmitantennas to multiple (R) receive antennas, where in general 1≦S≦min {T,R}. Each data stream may carry a packet in a transmission time interval(TTI) and may be referred to as a stream. A packet may also be referredto as a transport block, a codeword, etc. For clarity, certain aspectsof the techniques are specifically described below for transmission ofS=2 streams on the downlink from T=2 transmit antennas to R=2 receiveantennas, which is supported by high-speed downlink packet access(HSDPA) in WCDMA. The techniques may be extended to cover any number ofstreams, any number of transmit antennas, and any number of receiveantennas.

FIG. 1A shows a block diagram of a design of a transmitter 110 for aMIMO transmission. Transmitter 110 may be part of a base station fordownlink transmission or part of a UE for uplink transmission. A basestation may be an entity that communicates with the UEs and may also bereferred to as a Node B, an evolved Node B (eNB), an access point, etc.A UE may be stationary or mobile and may also be referred to as a mobilestation, a terminal, a station, a subscriber unit, etc. A UE may be acellular phone, a personal digital assistant (PDA), a wireless modem, awireless communication device, a handheld device, a laptop computer, acordless phone, a wireless local loop (WLL) station, a smart phone, anetbook, a smartbook, etc.

At transmitter 110, a channel encoder 112 a receives information bits{b₀} for a first stream (stream 0), processes (e.g., encodes andinterleaves) the information bits based on a coding scheme/code rateselected for the first stream, and provides code bits for the firststream. Similarly, a channel encoder 112 b receives information bits{b₁} for a second stream (stream 1), processes the information bitsbased on a coding scheme/code rate selected for the second stream, andprovides code bits for the second stream. Each channel encoder 112 mayimplement a Turbo code, a convolutional code, a block code, etc. Eachchannel encoder 112 may also perform puncturing and/or repetition toobtain the desired number of code bits. A symbol mapper 114 a maps thecode bits for the first stream to modulation symbols {s₀} based on amodulation order (e.g., QPSK, 16-QAM, or 64-QAM) selected for the firststream. A modulation order may also be referred to as a modulationscheme, a constellation, etc. A symbol mapper 114 b maps the code bitsfor the second stream to modulation symbols {s₁} based on a modulationorder selected for the second stream.

A precoder 116 performs precoding on the modulation symbols for thefirst and second streams based on a precoding matrix and providesprecoded symbols for two transmit antennas to CDMA modulators (Mod) 118a and 118 b. CDMA modulators 118 a and 118 b process (e.g., spread andscramble) their precoded symbols and provide output chips {c₀} and {c₁},respectively. Each CDMA modulator 118 may segment its precoded symbolsinto K sub-blocks, where K is the number of orthogonal variablespreading factor (OVSF) codes allocated to a UE. Each CDMA modulator 118may spread the precoded symbols in each sub-block with a different OVSFcode, combine the spread samples for all K OVSF codes, and provideoutput samples. Transmitter units (TMTR) 120 a and 120 b process (e.g.,convert to analog, amplify, filter, and frequency upconvert) the outputsamples from CDMA modulators 118 a and 118 b, respectively, and providemodulated signals, which are transmitted from antennas 122 a and 122 b,respectively.

Controller/processor 130 directs the operation of various processingunits at transmitter 110. Memory 132 stores data and program codes fortransmitter 110.

FIG. 1B shows a block diagram of a design of a receiver 150 for a MIMOtransmission. Receiver 150 may be part of a UE for downlink transmissionor part of a base station for uplink transmission. At receiver 150,antennas 152 a and 152 b receive the modulated signals from transmitter110 and provide received signals to receiver units (RCVR) 154 a and 154b, respectively. Each receiver unit 154 processes (e.g., filters,amplifies, frequency downconverts, and digitizes) its received signaland provides input samples to an equalizer 156. Equalizer 156 performsfiltering and equalization to account for multipath and providesequalized samples for the two receive antennas to CDMA demodulators(Demod) 158 a through 158 r. Each CDMA demodulator 158 processes (e.g.,descrambles and despreads) its equalized samples and provides receivedsymbols.

A MIMO detector 160 obtains the received symbols for both receiveantennas, performs MIMO detection on the received symbols, and computeslog-likelihood ratios (LLRs) for the code bits for the two streams. Achannel decoder 162 a receives and decodes the LLRs for the first streamand provides decoded data for the first stream. Similarly, a channeldecoder 162 b receives and decodes the LLRs for the second stream andprovides decoded data for the second stream. In general, the processingby CDMA demodulators 158, MIMO detector 160, and channel decoders 162 atreceiver 150 is complementary to the processing by CDMA modulators 118,precoder 116 and symbol mappers 114, and channel encoders 112 attransmitter 110.

Controller/processor 170 directs the operation of various processingunits at receiver 150. Memory 172 stores data and program codes forreceiver 150.

WCDMA supports a single stream (SS) mode and a dual stream (DS) mode. Inthe SS mode, a single stream may be precoded with a precoding vector andtransmitted from two transmit antennas. In the DS mode, two streams maybe precoded with a precoding matrix and transmitted from two transmitantennas.

To support data transmission on the downlink, a UE may report thefollowing parameters:

-   -   1. Selection of the SS mode or the DS mode,    -   2. Selection of a precoding vector for the SS mode or a        precoding matrix for the DS mode, and    -   3. Selection of CQI for each stream.

The UE may report precoding control information (PCI) indicative of theselected precoding vector or matrix, the SS/DS preference, and a CQI foreach stream to a base station. The base station may determine atransport format resource combination (TFRC) for each stream based onthe reported CQI for that stream and additional information such as theamount of data to send. The TFRC may be associated with a transportblock size (TBS), a particular number of OVSF codes, and a particularmodulation order to use for data transmission.

Table 1 shows an exemplary table of CQI versus TFRC for a case of 15OVSF codes and a step size of approximately 1.5 decibels (dB) (in termsof SINR) between CQI values in WCDMA. As shown in Table 1, both TBS andmodulation order are non-decreasing versus CQI. In the DS mode, one CQIis reported for each stream, each CQI has a value within a range of 0 to14, and there are 225 possible combinations of CQI₀ for the first streamand CQI₁ for the second stream. Each CQI corresponds to a specific TBSsize and a specific modulation order. In the SS mode, one CQI isreported for the single stream and has a value within a range of 0 to31. The SS/DS preference and one or more CQIs for one or two streams arecombined into a single 8-bit number that covers a total of 256possibilities.

TABLE 1 Transport CQI₁ or Block Size Modulation CQI₂ (TBS) Order 0 4592QPSK 1 4592 QPSK 2 5296 QPSK 3 7312 QPSK 4 9392 QPSK 5 11032 QPSK 614952 16-QAM 7 17880 16-QAM 8 21384 16-QAM 9 24232 16-QAM 10 2796064-QAM 11 32264 64-QAM 12 36568 64-QAM 13 39984 64-QAM 14 42192 64-QAM

FIG. 2 shows a pictorial representation of CQI₀ and CQI₁ for the DSmode. The horizontal axis represents CQI₀ for the first stream, and thevertical axis represents CQI₁ for the second stream. Each black dotrepresents a different combination of CQI₀ and CQI₁ for the two streams.For simplicity, only a subset of the 225 possible combinations of CQI₀and CQI₁ are shown in FIG. 2. The black dots are separated byapproximately 1.5 dB in each of the horizontal and vertical directions.One combination of CQI₀ and CQI₁ that maximizes the overall throughputfor the two streams may be selected.

In the SS mode, the received symbols from CDMA demodulators 158 may beexpressed as:y=Hps+n,  Eq (1)where

s is a modulation symbol for the single stream,

p is a precoding vector for the single stream,

H is a channel matrix for the wireless channel from transmitter 110 toreceiver 150,

y=[y₀ y₁]^(T) is a vector of received symbols from the two receiveantennas,

n is a vector of noise and interference observed by receiver 150, and

“^(T)” denotes a transpose.

The precoding vector p may be selected from a set of four possibleprecoding vectors p₀ through p₃, where

${p_{m} = \begin{bmatrix}{1/\sqrt{2}} \\w_{m}\end{bmatrix}},$for m=0, . . . , 3, with w₀=(1+j)/2, w₁=−w₀, w₂=(1−j)/2, and w₃=−w₂.

In the DS mode, the received symbols from CDMA demodulators 158 may beexpressed as:y=HPs+n,  Eq (2)where

s=[s₀ s_(j)]^(T) is a vector of modulation symbols for the two streams,and

P is a precoding matrix for the two streams.

The precoding matrix P may be selected from a set of four possibleprecoding matrices P₀ through P₃, where

${P_{m} = {{\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & {\mathbb{e}}^{{j\theta}_{m}}\end{bmatrix}} \cdot \begin{bmatrix}1 & 1 \\1 & {- 1}\end{bmatrix}}},{\theta_{0} = \frac{\pi}{4}},{\theta_{1} = \frac{7\pi}{4}},$and the remaining two precoding matrices may be obtained by swapping thecolumns of the first two precoding matrices. An equivalent channelmatrix H_(eq) may be defined as:H _(eq) =HP.  Eq (3)

In general, one or more streams may be transmitted with precoding (e.g.,as shown in equations (1) and (2)) or without precoding. If precoding isnot performed in the DS mode, then the received symbols may be expressedas y=Hs+n, and the equivalent channel matrix may be expressed asH_(eq)=H. For clarity, much of the description below assumes the use ofprecoding.

The noise and interference have a covariance matrix of R_(nn)=E{nn^(H)}, where “^(H)” denotes a conjugate transpose. The noise covariancematrix R_(nn) and the channel matrix H may both be estimated based on apilot channel transmitted by transmitter 110. The noise and interferencemay also be assumed to be additive white Gaussian noise (AWGN) with avariance of σ_(n) ². In this case, the noise covariance matrix may begiven as R_(nn)=σ_(n) ²I, where I is an identity matrix.

MIMO detector 160 may compute LLRs for the code bits based on thereceived symbols y, the equivalent channel matrix H_(eq), and the noisecovariance matrix R_(nn). In one design, MIMO detector 160 may computethe LLRs based on a max-log-map (MLM) algorithm, as follows:

$\begin{matrix}\begin{matrix}{{L\left( b_{k} \right)} = {\log\left( \frac{\Pr\left\{ {b_{k} = {0❘\overset{\_}{y}}} \right\}}{\Pr\left\{ {b_{k} = {1❘\overset{\_}{y}}} \right\}} \right)}} \\{= {\log\left( \frac{\sum\limits_{{s:b_{k}} = 0}\;{\Pr\left\{ {\overset{\_}{y}❘s} \right\}}}{\sum\limits_{{s:b_{k}} = 1}\;{\Pr\left\{ {\overset{\_}{y}❘s} \right\}}} \right)}} \\{\approx {\log\left( \frac{\max_{{s:b_{k}} = 0}{\Pr\left\{ {\overset{\_}{y}❘s} \right\}}}{\max_{{s:b_{k}} = 1}{\Pr\left\{ {\overset{\_}{y}❘s} \right\}}} \right)}} \\{= {{\min\limits_{{s:b_{k}} = 0}{d^{2}(s)}} - {\min\limits_{{s:b_{k}} = 1}{d^{2}(s)}}}}\end{matrix} & {{Eq}\mspace{14mu}(4)}\end{matrix}$where

L(b_(k)) is the LLR of code bit b_(k),

d(s)=∥ y− H _(eq)s∥,

y=R_(nn) ^(1/2)y is a vector of pre-whitened received symbols, and

H _(eq)=R_(nn) ^(1/2)H_(eq) is a channel matrix after noise whitening.

The MLM algorithm approximates the log-sum-exponent functions in therightmost part of the first row of equation (4) with max-log-mapfunctions. The MLM algorithm simplifies the computation of a maximuma-posteriori probability (MAP) algorithm by retaining only the dominantfactor contributing to the a-posteriori probabilities that the code bitunder consideration is 1 or 0. The MLM algorithm is a non-lineardetector that can outperform linear detectors such as zero-forcing (ZF)and minimum mean square error (MMSE) detectors. The MLM algorithm mayallow near-optimal detection of symbols transmitted via a MIMO channel.

The determination of CQI₀ and CQI₁ for the two streams in the DS modemay be formulated as follows. For a given channel matrix H and a givennoise covariance matrix R_(nn), a precoding matrix P as well as CQI₀ andCQI₁ may be selected to maximize the overall throughput for the twostreams. The throughput maximization may be expressed as:

$\begin{matrix}{{\max\limits_{{CQI}_{0},{CQI}_{1}}{\sum\limits_{i = 0}^{1}\;{{TBS}_{{CQI}_{i}} \cdot \left\lbrack {1 - {{BLER}_{i}\left( {H_{eq},R_{nn},{CQI}_{0},{CQI}_{1}} \right)}} \right\rbrack}}},} & {{Eq}\mspace{14mu}(5)}\end{matrix}$where

TBS_(CQI) is the TBS corresponding to CQI_(i) for stream i, with i=0, 1,and

BLER_(i) is a block error rate for stream i.

In equation (5), the summation provides the overall throughput for thetwo streams. The throughput of each stream may be determined based onthe TBS and the BLER of that stream. The TBS of each stream may bedetermined by the CQI of that stream, e.g., as shown in Table 1. TheBLER of each stream may be dependent on H_(eq), R_(nn), CQI₀ and CQI₁,as described below.

Algorithms to determine CQIs for MIMO transmission are typicallydesigned for linear detectors such as ZF and MMSE detectors. For alinear detector, the SINR per symbol at the output of the lineardetector may be computed. For example, the SINRs of the two streams inthe DS mode from an MMSE detector may be expressed as:SINR₀ =h _(eq,0) ^(H)(R _(nn) +h _(eq,1) h _(eq,1) ^(H))⁻¹ h _(eq,0),and  Eq (6)SINR₁ =h _(eq,1) ^(H)(R _(nn) +h _(eq,0) +h _(eq,0) h _(eq,0) ^(H))⁻¹ h_(eq,1),  Eq (7)where H_(eq)=[h_(eq,0) h_(eq,1)], SINR₀ is the SINR of stream 0, andSINR₁ is the SINR of stream 1. SINR of each stream may be mapped to aCQI based on a mapping table.

For a linear detector, different possible precoding vectors or matricesmay be evaluated. For each precoding vector or matrix, the equivalentchannel matrix H_(eq) may be computed based on that precoding vector ormatrix, the SINRs of the two streams may be computed based on theequivalent channel matrix and mapped to CQIs, and the overall throughputfor the two streams may be computed based on the TBS valuescorresponding to the CQIs. The precoding vector or matrix and the CQIswith the highest overall throughput may be selected and reported.

For the MLM detector, different possible precoding vectors or matricesmay be evaluated in similar manner as described above for a lineardetector. However, it may be difficult to define the SINRs of the twostreams due to the non-linear nature of the MLM detector. CQI algorithmsdesigned for a linear detector may be used for the MLM detector but maynot provide good performance. A good CQI algorithm for the MLM detectorshould take into account the nature of MLM detection and should reliablyestimate its maximum achievable throughput by efficiently extractingsufficient information from H_(eq), R_(nn), CQI₀ and CQI₁.

As shown in equation (5), the maximum overall throughput for the MLMdetector is dependent on the BLER of each stream. To solve equation (5),BLER contours for both streams may be generated for different TBS/CQIcombinations under various realizations of H_(eq) in an AWGN channel.

FIG. 3A shows an exemplary plot 310 of a 10% BLER contour for the firststream with 0.5 dB sample intervals for both TBS₀ for the first streamand TBS₁ for the second stream. FIG. 3B shows an exemplary plot 320 of a10% BLER contour for the second stream with 0.5 dB sample intervals forboth TBS₀ and TBS₁. In both FIGS. 3A and 3B, a cross mark at the bottomleft corner of the graph represents an operating point determined by aCQI algorithm for an MMSE detector (or an MMSE-CQI algorithm). Thisoperating point is defined by TBS₀ ^(MMSE) and TBS₁ ^(MMSE) selected forthe two streams by the MMSE-CQI algorithm.

The following observations can be made from the BLER contours in FIGS.3A and 3B. For the first observation, the BLER of the first stream isinsensitive to the TBS/CQI of the second stream if the modulation orderof the second stream is unchanged. If the modulation order of the secondstream is changed, then the BLER of the first stream may changedepending on H_(eq) and R_(nn). Similarly, the BLER of the second streamis affected by the modulation order for the first stream. This may implythat the BLER of stream i may be given as BLER_(i)(H_(eq), R_(nn),CQI_(i), Q_(j)), where j=1−i, and Q_(j) denotes the modulation order ofinterfering stream j.

For the second observation, if the modulation order of the interferingstream j is fixed, then the BLER of stream i may be approximated asfollows:BLER_(i)(H _(eq) ,R _(nn),CQI_(i) *,Q _(j))≈0,  Eq (8)BLER_(i)(H _(eq) ,R _(nn),CQI_(i) *,Q _(j))≈1,  Eq (9)where CQI_(i)*=max {m|BLER_(i)(H_(eq),R_(nn),m,Q_(j))≈0}. CQI_(i)* isthe maximum CQI value such that stream i can be decoded correctly forthe given H_(eq), R_(nn), and modulation order Q_(j) for interferingstream j. Equations (8) and (9) exploit the relatively large spacing (ofapproximately 1.5 dB) between two adjacent TBS/CQI values in Table 1.

The second observation implies that the BLER of stream i may beapproximated by a step function for an AWGN channel, with the BLER beingequal to 0 below some TBS threshold and equal to 1 above the TBSthreshold. This TBS threshold may be denoted as TBS_(i) ^(Q) and maycorrespond to the maximum number of information bits that can bereliably decoded per TTI for stream i when modulation order Q is usedfor the interfering stream.

For the third observation, the MLM detector has very low BLERs whenoperated at the operating point for the MMSE detector. For the MMSEdetector, TBS₀ ^(MMSE) and TBS₁ ^(MMSE) may be determined for the twostreams based on a look-up table that maps SINR to TBS based on anassumption of Gaussian noise. However, since the interfering streamimparts discrete interference, the MLM detector may exploit thisinformation and possibly support a higher TBS than the operating pointfor the MMSE detector. Hence, TBS₀ ^(MMSE) and TBS₁ ^(MMSE) may beviewed as a reference point, and improvement in TBS may be possible dueto more favorable discrete interference from modulation order Qε{QPSK,16QAM, 64QAM} for the given H_(eq) and R_(nn).

Based on the above observations, TBS₀ and TBS₁ may be determined for thetwo streams for the MLM detector by first determining feasible BLERregions. For the given H_(eq) and R_(nn), six TBS thresholds TBS₀^(QPSK), TBS₀ ^(16QAM), TBS₀ ^(64QAM), TBS₁ ^(QPSK), TBS₁ ^(16QAM), andTBS₁ ^(64QAM) may be determined.

FIG. 4A shows a plot of a feasible BLER region for the first stream. Thehorizontal axis represents TBS₀ for the first stream, and the verticalaxis represents TBS₁ for the second stream. Dashed lines 412, 414 and416 correspond to TBS₀ ^(64QAM), TBS₀ ^(16QAM), and TBS₀ ^(QPSK),respectively. A dashed line 422 corresponds to a TBS value at which themodulation order for the second stream switches from QPSK to 16-QAM. Adashed line 424 corresponds to a TBS value at which the modulation orderswitches from 16-QAM to 64-QAM. A line 426 corresponds to the maximumTBS value. A step-wise line 430 represents the TBS threshold fordifferent modulation orders. The BLER of the first stream isapproximately 1 above line 430 and is approximately 0 below line 430.The feasible BLER region for the first stream is below line 430.

FIG. 4B shows a plot of a feasible BLER region for the second stream.Dashed lines 452, 454 and 456 correspond to TBS₁ ^(64QAM), TBS₁ ^(16QAM)and TBS₁ ^(QPSK), respectively. Dashed lines 462 and 464 correspond toTBS values at which the modulation order for the first stream switchesfrom QPSK to 16-QAM and from 16-QAM to 64-QAM. A line 466 corresponds tothe maximum TBS value. A step-wise line 470 represents the TBS thresholdfor different modulation orders. The BLER of the second stream isapproximately 1 above line 470 and is approximately 0 below line 470.The feasible BLER region for the second stream is below line 470.

As shown in FIGS. 4A and 4B, the TBS threshold for each stream decreasesas the modulation order increases from QPSK to 16-QAM and 64-QAM. Thismeans that progressively larger TBS can be supported for stream i forprogressively lower modulation order on interfering stream j.

FIG. 4C shows a plot of an overall feasible BLER region formed by theintersection of the feasible BLER regions for the two streams in FIGS.4A and 4B. The overall feasible BLER region is shown with shading inFIG. 4C and covers TBS values such that the BLER is approximately 0 forboth streams. The highest overall throughput for both streams may bedetermined by (i) determining the overall throughput for the two streamsbased on TBS₀ and TBS₁ at each vertex (e.g., at points A, B, C, D and E)in FIG. 4C and (ii) selecting the combination of TBS₀ and TBS₁ with thelargest overall throughput.

As shown in FIGS. 4A to 4C, the overall feasible BLER region is definedby the six TBS thresholds shown in FIGS. 4A and 4B. The TBS thresholdfor stream i with modulation order Q for interfering stream j may bedetermined for the given H_(eq) and R_(nn). The required SINR fordifferent TBS values with a particular BLER (e.g., 10% BLER) for a Turbodecoder under Gaussian noise may be determined (e.g., via computersimulations or empirical analysis). The throughput achieved for stream 1with Gaussian noise may be improved due to more favorable non-Gaussiannoise resulting from discrete interference with modulation order Q usedfor stream j. This throughput improvement may be captured via the notionof constellation constrained capacity, which is capacity for a streamconstrained by a particular modulation order (or constellation) used forthe stream.

Equation (2) may be rewritten as follows:y=h _(eq,0) s ₀ +h _(eq,1) s ₁ +n.  Eq (10)As shown in equation (10), the two streams are transmitted via twosingle-input multiple-output (SIMO) channels having channel vectors ofh_(eq,0) and h_(eq,1).

The capacity of the SIMO channel for stream i with discreteinterference, which is also referred to as the mutual information, maybe expressed as:C(s _(i) ,y)=C(s _(j) ,y)−C(s _(j) ,h _(eq,j) s _(j) +n)+log₂(1+h_(eq,i) ^(H) R _(nn) ⁻¹ h _(eq,i)),  Eq (11)where

-   -   C(s_(j),y) and C(s_(j),h_(eq,j)s_(j)+n) are constellation        constrained capacities of SIMO channels for stream j with        discrete input s_(j) and Gaussian noise h_(eq,i)s_(i)+n and n,        respectively, and    -   C(s_(i),y) is the capacity of the SIMO channel for stream i with        discrete interference.

The capacity of the SIMO channel for stream i in equation (11) assumesthat modulation symbol s_(j) of stream i and noise n are Gaussian andthat modulation symbol s_(j) of interfering stream j is generated withmodulation order Q. The equivalent SINRs of the SIMO channels for streamj may be expressed as:SINR_(1,j) =h _(eq,j) ^(H)(R _(nn) +h _(eq,i) h _(eq,i) ^(H))⁻¹ h_(eq,j), and  Eq (12)SINR_(2,j) =h _(eq,j) ^(H) R _(nn) ⁻¹ h _(eq,j),  Eq (13)where

SINR_(1,j) is an equivalent SINR of the SIMO channel for C(s_(j), y),and

SINR_(2,j) is an equivalent SINR of the SIMO channel forC(s_(j),h_(eq,j)s_(j)+n).

Three look-up tables for constellation constrained capacity for QPSK,16-QAM, and 64-QAM in single-input single-output (SISO) channels may bedefined. SINR_(1,j) may be mapped to capacity C_(1,j) ^(Q) based on alook-up table for modulation order Q. SINR_(2,j) may also be mapped tocapacity C_(2,j) ^(Q) based on the look-up table for modulation order Q.The mapping of SINR to capacity may also be based on a suitableconstellation constrained capacity function for modulation order Q.Equation (11) may then be rewritten as:C(s _(i) ,y,Q)=C _(1,j) ^(Q) −C _(2,j) ^(Q)+log₂(1+h _(eq,i) ^(H) R_(nn) ⁻¹ h _(eq,i)),  Eq (14)where C(s_(i), y,Q) is the capacity of the SIMO channel for stream iwith modulation order Q used on interfering stream j.

As shown in equation (14), the capacity of the SIMO channel for stream iwith discrete interference includes two parts. The first part includesΔC_(j) ^(Q)=C_(1,j) ^(Q)−C_(2,j) ^(Q) and may be viewed as throughputdegradation due to discrete interference from stream j. A lowermodulation order leads to higher degradation, so that ΔC_(j)^(QPSK)≧ΔC_(j) ^(16QAM)≧ΔC_(j) ^(64QAM). The second part includeslog₂(1+h_(eq,i) ^(H)R_(nn) ⁻¹h_(eq,i)) and is a SIMO channel capacitywithout interference from interfering stream j.

The capacity C(s_(i),y) of stream i with discrete interference may bemapped to SINR based on an unconstrained capacity function, as follows:SINR_(i) ^(Q)=2^(C(s) ^(i) ^(,y,Q))−1,  Eq (15)where SINR_(i) ^(Q) is the SINR of stream i with modulation order Qbeing used on interfering stream j.

In one design, SINR_(i) ^(Q) may be mapped to a TBS threshold TBS_(i)^(Q) for stream i with modulation order Q for interfering stream j basedon a SINR-to-TBS mapping table. This SINR-to-TBS mapping table may beobtained empirically for different channel codes with a particulartarget BLER. In general, C(s_(i), y, Q) increases as the modulationorder of the interfering stream j decreases. This leads to TBS_(i)^(QPSK)≧TBS_(i) ^(16QAM)≧TBS_(i) ^(64QAM)≧TBS_(i) ^(MMSE). A larger TBSmay be requested for stream i by reducing the modulation order ofinterfering stream j, which is reflected in FIGS. 4A to 4C.

In another design, SINR may be mapped to TBS based on a function, whichmay be as follows:

$\begin{matrix}{{{TBS} = {480 \cdot N_{C} \cdot {\log_{2}\left( {1 + \frac{{SINR}^{0.8933}}{1.2871}} \right)}}},} & {{Eq}\mspace{14mu}(16)}\end{matrix}$where N_(C) is the number of OVSF codes. Equation (16) shows anexemplary function for mapping from SINR to TBS. Other functions mayalso be used to map SINR to TBS.

FIG. 5 shows plots of the TBS thresholds for stream 0. A vertical line512 represents TBS threshold TBS₀ ^(QPSK) for stream 0 with QPSK beingused for stream 1. A vertical line 514 represents TBS threshold TBS₀^(16QAM) for stream 0 with 16-QAM being used for stream 1. A line 516represents a TBS threshold that results in the target BLER based oncomputer simulations. As shown in FIG. 5, the TBS thresholds TBS₀^(QPSK) and TBS₀ ^(16QAM) estimated based on the computation inequations (11) to (14) may be optimistic. Hence, some TBS margins may beapplied in order to obtain the target BLER.

In one design, TBS_(i) ^(Q) may be mapped to CQI based on a look-uptable such as Table 1. The mapping of TBS to CQI may change due tovarious factors such as UE category, the number of OVSF codes, networkoperator, etc. Furthermore, information about modulation switchingpoints on a TBS mapping table may not be available.

In another design, SINR_(i) ^(Q) may be mapped to CQI based on a look-uptable. Operating in the SINR domain may improve performance since SINRmay be largely insensitive with respect to the issues listed above forthe TBS domain, especially in a well-designed system. Computersimulations show that the modulation switching points in the SINR domainare insensitive to the number of OVSF codes. For example, modulationswitching points in the SINR domain versus N_(C) may be as shown inTable 2. Furthermore, operating in the SINR domain may be more robustwhen information about modulation switching points on a TBS table is notavailable.

TABLE 2 Number of OVSF Codes QPSK → 16-QAM 16-QAM → 64-QAM N_(C) = 1SINR = 5 dB SINR = 12.6 dB N_(C) = 15 SINR = 5.5 dB SINR = 13 dB

FIG. 6 shows a plot of a feasible BLER region for stream 1 based onSINR. The horizontal axis represents SINR₀ for stream 0, and thevertical axis represents SINR₁ for stream 1. Dashed lines 612, 614 and616 correspond to three SINR thresholds SINR₁ ^(QPSK), SINR₁ ^(16QAM),and SINR₁ ^(64QAM) respectively, for stream 1. A dashed line 622corresponds to an SINR value at which the modulation order for stream 0switches from QPSK to 16-QAM. A dashed line 624 corresponds to a SINRvalue at which the modulation order switches from 16-QAM to 64-QAM. Aline 626 corresponds to the SINR value for the largest CQI value. Astep-wise line 630 represents the SINR threshold for differentmodulation orders. The BLER of stream 1 is approximately 1 above line630 and is approximately 0 below line 630. The feasible BLER region forstream 1 is below line 630.

The MLM-CQI algorithm described above may be used to determine CQIs withor without successive interference cancellation (SIC). For SIC, areceiver/UE may decode one stream at a time, typically starting with thestream having the best SINR or lowest BLER. If this stream is decodedcorrectly, then the interference due to the stream may be estimated(e.g., as h_(eq,0) s₀) and canceled from the received signals to obtaininterference-canceled signals (e.g., y−h_(eq,0) s₀). Theinterference-canceled signals (instead of the received signals) may thenbe processed to recover another stream. SIC may enlarge the feasibleBLER region of the stream recovered later and may push out the vertices.The BLER region for the stream recovered later with SIC may be predictedbased on the BLER regions for the two streams without SIC.

FIG. 7 shows a design of a process 700 for determining CQIs for twostreams in the DS mode. Initially, a channel matrix H and a noisecovariance matrix R_(nn) may be obtained (block 712). A precoding matrixP may be selected for evaluation (block 714). An equivalent channelmatrix H_(eq) may be computed based on the channel matrix H and theprecoding matrix P, e.g., as shown in equation (3) (block 716).

TBS thresholds for each stream may be determined based on the equivalentchannel matrix H_(eq), the noise covariance matrix R_(nn), and themodulation order Q of the interfering stream, e.g., as described above(block 718). Feasible BLER regions for both streams may be determinedbased on the TBS thresholds for these streams, e.g., as shown in FIGS.4A and 4B (block 720). The feasible BLER regions for the two streams maybe overlapped, and the vertices may be determined, e.g., as shown inFIG. 4C (block 722). The overall throughput of the two streams may bedetermined at each vertex (block 724). In one design, the TBS thresholdsfor a vertex may first be quantized to the closest TBS values in Table1, and the overall throughput for the vertex may be determined based onthe quantized TBS₀ and TBS₁ for the two streams. The vertex with thehighest overall throughput may be identified, and the corresponding TBSthresholds TBS₀ ^(Q) and TBS₁ ^(Q) for this vertex may be saved (block726).

A determination is made whether all precoding matrices have beenevaluated (block 728). If the answer is ‘No’, then the process returnsto block 714 to select another precoding matrix for evaluation.Otherwise, if all precoding matrices have been evaluated, then theprecoding matrix P with the highest overall throughput and thecorresponding TBS₀ and TBS₁ for the two streams may be retrieved (block730). TBS₀ and TBS₁ may be mapped to CQI₀ and CQI₁, respectively, forthe two streams (block 732). The precoding matrix P and CQI₀ and CQI₁for the two streams may be reported (block 734).

As noted above, the SS mode and the DS mode may be supported. In thiscase, the throughput of one stream may be computed for each of theavailable precoding vectors. The highest throughput for one stream inthe SS mode may be compared against the highest overall throughput fortwo streams in the DS mode. If the highest throughput for one stream ishigher than the highest overall throughput for two streams, then the SSmode may be selected, and the corresponding precoding vector and CQI forthe one stream with the highest throughput may be reported. Otherwise,the DS mode may be selected, and the corresponding precoding matrix andCQI₀ and CQI₁ for the two streams with the highest overall throughputmay be reported.

For a brute-force method, all 225 possible combinations of CQI₀ and CQI₁may be evaluated for each possible precoding matrix. For each CQIcombination, BLER₀ and BLER₁ may be computed based on the channel matrixH, the precoding matrix P, the noise covariance matrix R_(nn), and CQI₀and CQI₁ for that combination. The overall throughput for each CQIcombination may then be computed based on TBS₀ and TBS₁ corresponding toCQI₀ and CQI₁ as well as BLER₀ and BLER₁, e.g., as shown in equation(5). The process may be repeated for each possible precoding matrix. Theprecoding matrix and CQI₀ and CQI₁ with the highest overall throughputmay be selected. Computation may be extensive due to the many (e.g.,225) CQI combinations to evaluate for each precoding matrix.

The design shown in FIG. 7 may greatly reduce computation over thebrute-force method. In particular, the TBS thresholds may be computedfor only certain CQI values (e.g., CQI values 0, 6 and 10 in Table 1)corresponding to a change in modulation order. Furthermore, the BLERfunction may be approximated with a step function. This may greatlysimplify the determination of CQI₀ and CQI₁ for the two streams for theMLM detector.

For clarity, the techniques for determining CQIs for two streams havebeen described for a MLM detector. The techniques may also be used forother non-linear detectors such as a maximum likelihood (ML) detector, aMLM detector with SIC (or MLM-SIC detector), a ML detector with SIC (orML-SIC detector), a sphere detector, etc.

FIG. 8 shows a design of a process 800 for reporting CQIs. Process 800may be performed by a UE (as described below) or by some other entity.The UE may determine at least one parameter based on at least oneconstellation constrained capacity function (block 812). The UE maydetermine CQIs for multiple streams for a non-linear detector based onthe at least one parameter (block 814). The non-linear detector maycomprise a MLM detector, or a ML detector, or a MLM-SIC detector, or aML-SIC detector, or a sphere detector, or some other non-linear detectorhaving better performance than a linear detector such as a MMSE detectoror a ZF detector. The UE may also select a precoding matrix (e.g.,jointly with the CQIs) based on the at least one parameter (block 816).The UE may report the selected precoding matrix and the CQIs for themultiple streams (block 818). The UE may thereafter receive atransmission of the multiple streams, which may be transmitted based onthe selected precoding matrix and the CQIs (block 820).

In one design, the multiple streams may comprise a first stream and asecond stream. In one design of block 812, the UE may determine at leastone first threshold for the first stream and at least one secondthreshold for the second stream based on the at least one constellationconstrained capacity function. Each first threshold may be associatedwith a different modulation order and may correspond to a maximum numberof information bits for the first stream when the associated modulationorder is used for the second stream. Similarly, each second thresholdmay be associated with a different modulation order and may correspondto a maximum number of information bits for the second stream when theassociated modulation order is used for the first stream. The first andsecond thresholds may relate to TBS (e.g., as shown in FIGS. 4A to 4C),or SINR (e.g., as shown in FIG. 6), or some other parameter. In onedesign, the UE may determine the first and second thresholds basedfurther on a precoding matrix, a channel matrix, and a noise covariancematrix, as described above. The first and second thresholds may bedetermined based further on SIC being performed for the multiplestreams.

In one design, the UE may determine a first constellation constrainedcapacity (e.g., C_(1,j) ^(Q)) of the SIMO channel for the second streamj with a particular modulation order Q being used for the second stream,Gaussian noise due to the first stream, and Gaussian channel noise,e.g., based on equation (12) and an SINR to capacity look-up table formodulation order Q. The UE may determine a second constellationconstrained capacity (e.g., C_(2,j) ^(Q)) of the SIMO channel for thesecond stream with the particular modulation order being used for thesecond stream and Gaussian channel noise, e.g., based on equation (13)and the SINR to capacity look-up table for modulation order Q. The UEmay determine a first capacity of the SIMO channel for the first streami with Gaussian channel noise, e.g., log₂(1+h_(eq,i) ^(H)R_(nn)⁻¹h_(eq,i)). The UE may determine a second capacity (e.g., C(s_(i),y,Q))of the SIMO channel for the first stream with discrete interference fromthe second stream based on the first and second constellationconstrained capacities and the first capacity, e.g., as shown inequation (14). The UE may determine a first threshold for the firststream with the particular modulation order Q being used for the secondstream based on the second capacity.

In one design, the UE may determine a plurality of vertices of a graphformed based on the at least one first threshold on a horizontal axisand the at least one second threshold on a vertical axis (e.g., as shownin FIG. 4C). The UE may determine an overall throughput for the firstand second streams at each of the plurality of vertices. The UE maydetermine a vertex associated with the highest overall throughput amongthe plurality of vertices. The UE may then determine CQIs for the firstand second streams based on a first threshold and a second thresholdcorresponding to the vertex associated with the highest overallthroughput.

In one design, the UE may evaluate different precoding matrices that canbe used for the first and second streams. The UE may repeat thedetermining a plurality of vertices, the determining an overallthroughput, and the determining a vertex associated with the highestoverall throughput for each of a plurality of precoding matrices. The UEmay select a precoding matrix associated with the highest overallthroughput among the plurality of precoding matrices. The UE maydetermine the CQIs for the first and second streams based on the firstand second thresholds corresponding to the vertex associated with thehighest overall throughput for the selected precoding matrix. In onedesign, the UE may map the first threshold to a first CQI for the firststream and may map the second threshold to a second CQI for the secondstream.

In one design, the UE may select a single stream or multiple streams fortransmission. The UE may determine throughput for a single stream foreach of a plurality of precoding vectors. The UE may also determine theoverall throughput for multiple (e.g., two) streams for each of aplurality of precoding matrices. The UE may select transmission of thesingle stream if the highest throughput for the single stream is higherthan the highest overall throughput for the multiple streams.Alternatively, the UE may select transmission of the multiple streams ifthe highest overall throughput for the multiple streams is higher thanthe highest throughput for the single stream.

FIG. 9 shows a design of an apparatus 900 for reporting CQIs. Apparatus900 includes a module 912 to determine at least one parameter based onat least one constellation constrained capacity function, a module 914to determine CQIs for multiple streams for a non-linear detector basedon the at least one parameter, a module 916 to select a precoding matrix(e.g., jointly with CQIs) based on the at least one parameter, a module918 to report the selected precoding matrix and the CQIs for themultiple streams, and a module 920 to receive a transmission of themultiple streams transmitted based on the selected precoding matrix andthe CQIs.

FIG. 10 shows a design of a process 1000 for receiving CQIs. Process1000 may be performed by a base station (as described below) or by someother entity. The base station may receive CQIs for multiple (e.g., two)streams from a UE (block 1012). The CQIs may be determined for anon-linear detector by the UE based on at least one parameter, which maybe determined based on at least one constellation constrained capacityfunction. The base station may also receive a precoding matrix selectedby the UE (e.g., jointly with the CQIs) based on the at least oneparameter (block 1014). The base station may transmit the multiplestreams to the UE based on the CQIs and the precoding matrix (block1016).

FIG. 11 shows a design of an apparatus 1100 for receiving CQIs.Apparatus 1100 includes a module 1112 to receive CQIs for multiplestreams from a UE, with the CQIs being determined for a non-lineardetector by the UE based on at least one parameter determined based onat least one constellation constrained capacity function, a module 1114to receive a precoding matrix selected by the UE (e.g., jointly with theCQIs) based on the at least one parameter, and a module 1116 to transmitthe multiple streams to the UE based on the CQIs and the precodingmatrix.

The modules in FIGS. 9 and 11 may comprise processors, electronicdevices, hardware devices, electronic components, logical circuits,memories, software codes, firmware codes, etc., or any combinationthereof.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communication, comprising:determining at least one parameter based on at least one constellationconstrained capacity function; and determining channel quantityindicators (CQIs) for multiple streams for a non-linear detector basedon the at least one parameter, wherein the multiple streams comprise afirst stream and a second stream, wherein the determining the at leastone parameter comprises determining at least one first threshold for thefirst stream and at least one second threshold for the second streambased on the at least one constellation constrained capacity function,each first threshold corresponding to a different modulation order forthe second stream, and each second threshold corresponding to adifferent modulation order for the first stream, wherein the determiningthe at least one first threshold and the at least one second thresholdcomprises determining the at least one first threshold and the at leastone second threshold based further on a precoding matrix and a channelmatrix, and wherein the determining the CQIs for the multiple streamscomprises evaluating each of a plurality of precoding matrices,selecting a precoding matrix associated with a highest overallthroughput among the plurality of precoding matrices, and determiningCQIs for the first and second streams based on a first threshold and asecond threshold corresponding to the highest overall throughput for theselected precoding matrix.
 2. The method of claim 1, wherein the atleast one first threshold and the at least one second threshold relateto transport block size (TBS).
 3. The method of claim 1, wherein the atleast one first threshold and the at least one second threshold relateto signal-to-noise-and-interference ratio (SINR).
 4. The method of claim1, wherein the determining the at least one first threshold and the atleast one second threshold comprises determining the at least one firstthreshold and the at least one second threshold based further on a noisecovariance matrix.
 5. The method of claim 1, further comprising:determining throughput for a single stream for each of a plurality ofprecoding vectors; determining overall throughput for the multiplestreams for each of a plurality of precoding matrices; selectingtransmission of the single stream if a highest throughput for the singlestream is higher than a highest overall throughput for the multiplestreams; and selecting transmission of the multiple streams if thehighest overall throughput for the multiple streams is higher than thehighest throughput for the single stream.
 6. The method of claim 1,wherein the non-linear detector comprises a max-log-map (MLM) detector,or a maximum likelihood (ML) detector, or a MLM detector with successiveinterference cancellation (SIC), or a ML detector with SIC, or a spheredetector.
 7. The method of claim 1, wherein the at least one firstparameter is determined based further on successive interferencecancellation (SIC) being performed for the multiple streams.
 8. A methodfor wireless communication, comprising: determining at least oneparameter based on at least one constellation constrained capacityfunction; and determining channel quantity indicators (CQIs) formultiple streams for a non-linear detector based on the at least oneparameter, wherein the multiple streams comprise a first stream and asecond stream, wherein the determining the at least one parametercomprises determining at least one first threshold for the first streamand at least one second threshold for the second stream based on the atleast one constellation constrained capacity function, each firstthreshold corresponding to a different modulation order for the secondstream, and each second threshold corresponding to a differentmodulation order for the first stream, wherein the determining the atleast one first threshold and the at least one second thresholdcomprises determining a first constellation constrained capacity of achannel for the second stream with a particular modulation order beingused for the second stream, Gaussian noise due to the first stream, andGaussian channel noise, determining a second constellation constrainedcapacity of the channel for the second stream with the particularmodulation order being used for the second stream and Gaussian channelnoise, determining a first capacity of a channel for the first streamwith Gaussian channel noise, determining a second capacity of thechannel for the first stream with discrete interference from the secondstream based on the first and second constellation constrainedcapacities and the first capacity, and determining a first threshold forthe first stream with the particular modulation order being used for thesecond stream based on the second capacity.
 9. A method for wirelesscommunication, comprising: determining at least one parameter based onat least one constellation constrained capacity function; anddetermining channel quantity indicators (CQIs) for multiple streams fora non-linear detector based on the at least one parameter, wherein themultiple streams comprise a first stream and a second stream, whereinthe determining the at least one parameter comprises determining atleast one first threshold for the first stream and at least one secondthreshold for the second stream based on the at least one constellationconstrained capacity function, each first threshold corresponding to adifferent modulation order for the second stream, and each secondthreshold corresponding to a different modulation order for the firststream, wherein the determining the CQIs for the multiple streamscomprises determining a plurality of vertices of a graph formed based onthe at least one first threshold on a horizontal axis and the at leastone second threshold on a vertical axis, determining an overallthroughput for the first and second streams at each of the plurality ofvertices, determining a vertex associated with a highest overallthroughput among the plurality of vertices, and determining CQIs for thefirst and second streams based on a first threshold and a secondthreshold corresponding to the vertex associated with the highestoverall throughput.
 10. The method of claim 9, wherein the determiningthe CQIs for the multiple streams further comprises repeating thedetermining a plurality of vertices, the determining an overallthroughput, and the determining a vertex associated with a highestoverall throughput for each of a plurality of precoding matrices,selecting a precoding matrix associated with a highest overallthroughput among the plurality of precoding matrices, and determiningthe CQIs for the first and second streams based on the first thresholdand the second threshold corresponding to the vertex associated with thehighest overall throughput for the selected precoding matrix.
 11. Themethod of claim 10, wherein the determining the CQIs for the first andsecond streams comprises mapping the first threshold to a first CQI forthe first stream, and mapping the second threshold to a second CQI forthe second stream.
 12. The method of claim 10, further comprising:reporting the selected precoding matrix and the CQIs for the first andsecond streams; and receiving a transmission of the first and secondstreams transmitted based on the selected precoding matrix and the CQIs.13. An apparatus for wireless communication, comprising: means fordetermining at least one parameter based on at least one constellationconstrained capacity function; and means for determining channelquantity indicators (CQIs) for multiple streams for a non-lineardetector based on the at least one parameter, wherein the multiplestreams comprise a first stream and a second stream, wherein the meansfor determining the at least one parameter comprises means fordetermining at least one first threshold for the first stream and atleast one second threshold for the second stream based on the at leastone constellation constrained capacity function, each first thresholdcorresponding to a different modulation order for the second stream, andeach second threshold corresponding to a different modulation order forthe first stream, wherein the means for determining the at least onefirst threshold and the at least one second threshold comprises meansfor determining the at least one first threshold and the at least onesecond threshold based further on a precoding matrix and a channelmatrix, and wherein the means for determining the CQIs for the multiplestreams comprises means for evaluating each of a plurality of precodingmatrices, means for selecting a precoding matrix associated with ahighest overall throughput among the plurality of precoding matrices,and means for determining CQIs for the first and second streams based ona first threshold and a second threshold corresponding to the highestoverall throughput for the selected precoding matrix.
 14. The apparatusof claim 13, wherein the means for determining the at least one firstthreshold and the at least one second threshold comprises means fordetermining the at least one first threshold and the at least one secondthreshold based further on a noise covariance matrix.
 15. An apparatusfor wireless communication, comprising: means for determining at leastone parameter based on at least one constellation constrained capacityfunction; and means for determining channel quantity indicators (CQIs)for multiple streams for a non-linear detector based on the at least oneparameter, wherein the multiple streams comprise a first stream and asecond stream, wherein the means for determining the at least oneparameter comprises means for determining at least one first thresholdfor the first stream and at least one second threshold for the secondstream based on the at least one constellation constrained capacityfunction, each first threshold corresponding to a different modulationorder for the second stream, and each second threshold corresponding toa different modulation order for the first stream, wherein the means fordetermining the at least one first threshold and the at least one secondthreshold comprises means for determining a first constellationconstrained capacity of a channel for the second stream with aparticular modulation order being used for the second stream, Gaussiannoise due to the first stream, and Gaussian channel noise, means fordetermining a second constellation constrained capacity of the channelfor the second stream with the particular modulation order being usedfor the second stream and Gaussian channel noise, means for determininga first capacity of a channel for the first stream with Gaussian channelnoise, means for determining a second capacity of the channel for thefirst stream with discrete interference from the second stream based onthe first and second constellation constrained capacities and the firstcapacity, and means for determining a first threshold for the firststream with the particular modulation order being used for the secondstream based on the second capacity.
 16. An apparatus for wirelesscommunication, comprising: means for determining at least one parameterbased on at least one constellation constrained capacity function; andmeans for determining channel quantity indicators (CQIs) for multiplestreams for a non-linear detector based on the at least one parameter,wherein the multiple streams comprise a first stream and a secondstream, wherein the means for determining the at least one parametercomprises means for determining at least one first threshold for thefirst stream and at least one second threshold for the second streambased on the at least one constellation constrained capacity function,each first threshold corresponding to a different modulation order forthe second stream, and each second threshold corresponding to adifferent modulation order for the first stream, wherein the means fordetermining the CQIs for the multiple streams comprises means fordetermining a plurality of vertices of a graph formed based on the atleast one first threshold on a horizontal axis and the at least onesecond threshold on a vertical axis, means for determining an overallthroughput for the first and second streams at each of the plurality ofvertices, means for determining a vertex associated with a highestoverall throughput among the plurality of vertices, and means fordetermining CQIs for the first and second streams based on a firstthreshold and a second threshold corresponding to the vertex associatedwith the highest overall throughput.
 17. The apparatus of claim 16,wherein the means for determining the CQIs for the multiple streamsfurther comprises means for repeating the determining a plurality ofvertices, the determining an overall throughput, and the determining avertex associated with a highest overall throughput for each of aplurality of precoding matrices, means for selecting a precoding matrixassociated with a highest overall throughput among the plurality ofprecoding matrices, and means for determining the CQIs for the first andsecond streams based on the first threshold and the second thresholdcorresponding to the vertex associated with the highest overallthroughput for the selected precoding matrix.
 18. An apparatus forwireless communication, comprising: at least one processor configured todetermine at least one parameter based on at least one constellationconstrained capacity function, and to determine channel quantityindicators (CQIs) for multiple streams for a non-linear detector basedon the at least one parameter, wherein the multiple streams comprise afirst stream and a second stream, wherein the at least one processor isconfigured to determine at least one first threshold for the firststream and at least one second threshold for the second stream based onthe at least one constellation constrained capacity function, each firstthreshold corresponding to a different modulation order for the secondstream, and each second threshold corresponding to a differentmodulation order for the first stream, wherein the at least oneprocessor is configured to determine the at least one first thresholdand the at least one second threshold based further on a precodingmatrix and a channel matrix, and wherein the at least one processor isconfigured to evaluate each of a plurality of precoding matrices, toselect a precoding matrix associated with a highest overall throughputamong the plurality of precoding matrices, and to determine CQIs for thefirst and second streams based on a first threshold and a secondthreshold corresponding to the highest overall throughput for theselected precoding matrix.
 19. The apparatus of claim 18, wherein the atleast one processor is configured to determine the at least one firstthreshold and the at least one second threshold based further on a noisecovariance matrix.
 20. An apparatus for wireless communication,comprising: at least one processor configured to determine at least oneparameter based on at least one constellation constrained capacityfunction, and to determine channel quantity indicators (CQIs) formultiple streams for a non-linear detector based on the at least oneparameter, wherein the multiple streams comprise a first stream and asecond stream, wherein the at least one processor is configured todetermine at least one first threshold for the first stream and at leastone second threshold for the second stream based on the at least oneconstellation constrained capacity function, each first thresholdcorresponding to a different modulation order for the second stream, andeach second threshold corresponding to a different modulation order forthe first stream, wherein the at least one processor is configured todetermine a first constellation constrained capacity of a channel forthe second stream with a particular modulation order being used for thesecond stream, Gaussian noise due to the first stream, and Gaussianchannel noise, determine a second constellation constrained capacity ofthe channel for the second stream with the particular modulation orderbeing used for the second stream and Gaussian channel noise, determine afirst capacity of a channel for the first stream with Gaussian channelnoise, to determine a second capacity of the channel for the firststream with discrete interference from the second stream based on thefirst and second constellation constrained capacities and the firstcapacity, and determine a first threshold for the first stream with theparticular modulation order being used for the second stream based onthe second capacity.
 21. An apparatus for wireless communication,comprising: at least one processor configured to determine at least oneparameter based on at least one constellation constrained capacityfunction, and to determine channel quantity indicators (CQIs) formultiple streams for a non-linear detector based on the at least oneparameter, wherein the multiple streams comprise a first stream and asecond stream, wherein the at least one processor is configured todetermine at least one first threshold for the first stream and at leastone second threshold for the second stream based on the at least oneconstellation constrained capacity function, each first thresholdcorresponding to a different modulation order for the second stream, andeach second threshold corresponding to a different modulation order forthe first stream, wherein the at least one processor is configured todetermine a plurality of vertices of a graph formed based on the atleast one first threshold on a horizontal axis and the at least onesecond threshold on a vertical axis, determine an overall throughput forthe first and second streams at each of the plurality of vertices, todetermine a vertex associated with a highest overall throughput amongthe plurality of vertices, and determine CQIs for the first and secondstreams based on a first threshold and a second threshold correspondingto the vertex associated with the highest overall throughput.
 22. Theapparatus of claim 21, wherein the at least one processor is configuredto repeat determining a plurality of vertices, determining an overallthroughput, and determining a vertex associated with a highest overallthroughput for each of a plurality of precoding matrices, select aprecoding matrix associated with a highest overall throughput among theplurality of precoding matrices, and determine the CQIs for the firstand second streams based on the first threshold and the second thresholdcorresponding to the vertex associated with the highest overallthroughput for the selected precoding matrix.
 23. A computer programproduct, comprising: a non-transitory computer-readable mediumcomprising: code for causing at least one computer to determine at leastone parameter based on at least one constellation constrained capacityfunction, and code for causing the at least one computer to determinechannel quantity indicators (CQIs) for multiple streams for a non-lineardetector based on the at least one parameter, wherein the multiplestreams comprise a first stream and a second stream, wherein thedetermining the at least one parameter comprises determining at leastone first threshold for the first stream and at least one secondthreshold for the second stream based on the at least one constellationconstrained capacity function, each first threshold corresponding to adifferent modulation order for the second stream, and each secondthreshold corresponding to a different modulation order for the firststream, wherein the determining the at least one first threshold and theat least one second threshold comprises determining the at least onefirst threshold and the at least one second threshold based further on aprecoding matrix and a channel matrix, and wherein the determining theCQIs for the multiple streams comprises evaluating each of a pluralityof precoding matrices, selecting a precoding matrix associated with ahighest overall throughput among the plurality of precoding matrices,and determining CQIs for the first and second streams based on a firstthreshold and a second threshold corresponding to the highest overallthroughput for the selected precoding matrix.
 24. A computer programproduct, comprising: a non-transitory computer-readable mediumcomprising: code for causing at least one computer to determine at leastone parameter based on at least one constellation constrained capacityfunction, and code for causing the at least one computer to determinechannel quantity indicators (CQIs) for multiple streams for a non-lineardetector based on the at least one parameter, wherein the multiplestreams comprise a first stream and a second stream, wherein thedetermining the at least one parameter comprises determining at leastone first threshold for the first stream and at least one secondthreshold for the second stream based on the at least one constellationconstrained capacity function, each first threshold corresponding to adifferent modulation order for the second stream, and each secondthreshold corresponding to a different modulation order for the firststream, wherein the determining the at least one first threshold and theat least one second threshold comprises determining a firstconstellation constrained capacity of a channel for the second streamwith a particular modulation order being used for the second stream,Gaussian noise due to the first stream, and Gaussian channel noise,determining a second constellation constrained capacity of the channelfor the second stream with the particular modulation order being usedfor the second stream and Gaussian channel noise, determining a firstcapacity of a channel for the first stream with Gaussian channel noise,determining a second capacity of the channel for the first stream withdiscrete interference from the second stream based on the first andsecond constellation constrained capacities and the first capacity, anddetermining a first threshold for the first stream with the particularmodulation order being used for the second stream based on the secondcapacity.
 25. A computer program product, comprising: a non-transitorycomputer-readable medium comprising: code for causing at least onecomputer to determine at least one parameter based on at least oneconstellation constrained capacity function, and code for causing the atleast one computer to determine channel quantity indicators (CQIs) formultiple streams for a non-linear detector based on the at least oneparameter, wherein the multiple streams comprise a first stream and asecond stream, wherein the determining the at least one parametercomprises determining at least one first threshold for the first streamand at least one second threshold for the second stream based on the atleast one constellation constrained capacity function, each firstthreshold corresponding to a different modulation order for the secondstream, and each second threshold corresponding to a differentmodulation order for the first stream, wherein the determining the CQIsfor the multiple streams comprises determining a plurality of verticesof a graph formed based on the at least one first threshold on ahorizontal axis and the at least one second threshold on a verticalaxis, determining an overall throughput for the first and second streamsat each of the plurality of vertices, determining a vertex associatedwith a highest overall throughput among the plurality of vertices, anddetermining CQIs for the first and second streams based on a firstthreshold and a second threshold corresponding to the vertex associatedwith the highest overall throughput.